1. Field of the Invention
The present invention relates to a technique enabling, in a gateway device that encrypts and decrypts an e-mail, a transmitting/receiving client to safely use an e-mail encryption system, even if a transmission/reception error occurs between the gateway device and a mail transmission/reception server.
2. Description of the Related Art
Currently, information is frequently exchanged by e-mails. However, because transmission and reception of e-mails are carried out through unspecified communication paths, it is possible that the e-mail might be electrically intercepted or altered in the middle of the communication path. An e-mail encryption system that encrypts e-mails is being developed in order to enable the transmitting/receiving client to safely use the e-mail system.
A method for easily and conveniently using the e-mail encryption system includes a method of interposing a gateway device, which encrypts and decrypts e-mails, between a client device and a mail transmission/reception server. The gateway device also serves as an easy and convenient mail transmission/reception server.
However, a transmission error might occur when the gateway device transmits an encrypted mail to the mail transmission server. In this case, the transmitting client is unable to know about the transmission error. The transmitting client is then unable to transmit the encrypted mail to the destination, is unable to know about the transmission error, and thus cannot safely use the e-mail encryption system.
Reception error might occur when the gateway device receives an encrypted mail from the mail reception server. The gateway device might be able to receive at least one encrypted mail from the mail reception server in this case. However, if the communication between the gateway device and the client device also becomes an error, the receiving client cannot receive a plain text mail from the gateway device. The receiving client then cannot receive the plain text mail from the source and thus cannot safely use the e-mail encryption system.